gehacktes ///

0026Building a Faux Neon Sign Using LED Strips (Part 2)

LED strips that look like neon tubes? Terrific! I’ve always wanted to build a neon sign! ´

CNC Milling Electronics Hardware Projects LEDs

As a quick recap, at the end of part 1 there were 4 things that bothered me:

Let’s try to fix the thin letters first.

Outlines for the Letters!

Doing a bit of research1 made me realise that there are two common ways to avoid the “my letters are looking thin” problem:

Variant 1 was quickly ruled out because of too much work: I would have had to completely rework the existing letters and LED strips.

Variant 2 however looked interesting: Maybe I could cut the outlines from polystyrene on the CNC mill? And if I included a 5mm wide cut-out in the centre, the LED strips would be perfectly aligned.

Outline prototype. The centre cut-out is exactly the width of the LED strip.For testing, I could simply slip the outline over the strip segments without having to remove them from the base plate. Nice!Note that some of the strip segments were a bit too short (as seen at the top arc of the “a” for example).

So far so good! And there even was an additional benefit I hadn’t thought of yet: When the outline layer was glued to the base plate it would help keeping the strips in position. Apart from making the whole setup more sturdy this should also finally solve the problem with the question mark’s dot!

But now it became apparent that the length of the segments did not always match the length of the strokes in the original drawing: The LED strip can only be cut about every 5cm, so some of the strips turned out shorter than originally planned. Up until now I hadn’t cared: Nobody would have noticed the difference, as the sign contained no reference to the original drawing. But with the outlines added this was no longer true: Now the differences in length became obvious.

The only way to fix this issue was to revise the drawing before using it as template for the milling process, adjusting the length of all strokes to be a multiples of 5cm. I decided to use this opportunity to also slightly tweak the form of some curves, making them look nicer when displayed with a thick outline.

Based on the updated drawings I could finally mill the outlines:

Because of the size of the mill’s work area three separate passes were needed: One for “W”, one for “as”, and a final one for “?“.

Milling the final outlines. With a bit of rotating an moving the individual parts it was possible to cut both “as” and “?” from a single 50x40 plate.Note the “tabs” spaced at regular intervals along the cuts: They make sure that all the parts stay in place during the milling process. When the milling is completed, you simply break or cut them away.

Fixing the Light Leaking Issue

Now that the biggest problem was out of the way I tackled the two remaining issues: Light leaking from the ends of the strips, and dark sections where the power wires had been attached.

My first idea was to simply cover the ends of the strips with some material. My go-to solution for covering anything is electrical tape, so I tried this first. Using white tape looked decent – but there was still light leaking through the tape.

Next try: Black tape. Now this did block all the light – but the black tape on the white strips looked hideous.

It was not until the following day that the obvious solution occurred to me: Why not simply build a tape sandwich? A layer of black tape covered by a layer of white tape on top should block all the light and still look acceptable:

End covers made of two layers of electrical tape. The strip at the right already has its cover applied – note the striking difference in how much light is visible on the black mat.In total I had to make 12 covers (for 6 strips).

Another problem solved!

Rethinking the Power Wire Connections

This left me with one final problem: The power wire connections.

The way I had attached the power wires to the strip segments worked perfectly in that the wires were completely invisible. However, as described earlier it required the removal of some LEDs which made these sections look noticeably darker (when the strip was lit).

There had to be a better method of attaching the power wires – time to experiment!

First try: Cutting a flap at one of the “cutting points” along the silicone strip where the solder pads are located. Removing the inner silicone then allows access to the solder pads, so that wires can be attached without having to actually cut the inner LED strip (thus without having to remove any LEDs).Like in the original solution the wires invisibly leave the strip at the bottom. The flap itself can be covered with electrical tape.One problem with this approach: Light leaking through the gaps next to the flap.

The first try was already an improvement to the original approach, but implementing it was rather time-consuming and involved. However, the underlying principle of using solder pads not at the end somewhere along the strip looked promising, so I tried to refine it:

Second try: Again a “flap” at one of the strip’s cutting points. However, this time the opening is cut from the other side, revealing the back side of the internal LED strip. The solder pads are accessible from this side as well, and cutting the flap at the back side is way easier because there is no inner silicone that needs to be removed.Accessing the solder pads from the back side is dead simple, making soldering the wires a breeze.With the flap positioned at the back side of the LEDs there is almost no light shining through the gaps (I didn’t take a photo of the strip while lit, so you just have to believe me). The only downside of this approach is that the wires create a small bulge in the strip – but it turned out to be as good as invisible when the strips were mounted to the sign.

This was the approach I decided to use. Now I had to implement it on all segments used for the letters on the sign. At first I cut off the hollow end from each strip, where the power wires had been attached so far. Of course this made the existing segments shorter – but I had to adjust the lengths of the segments to better fit the new outlines anyway2.

Here’s a sneak peak of how the cabling looks at the backside of the finished sign:

I don’t have a photo of the completed yellow / grey version of the sign, but this comes close.

I’m Finally Done – or am I?

Leaking ends covered, unlit (and wobbly) sections removed, thick outline added – by now I had managed to fix all my gripes.

However, the sign still didn’t look right.

It took me some time to actually understand the root cause: Because the outlines (grey) were darker than the base plate (yellow), when the sign was lit in a dim room the outlines merely looked like dark shadows around the bright faux neon letters, making them again look thin and fragile.

I don’t have a photo of the completed yellow / grey version of the sign, but this comes close.

Changing the Colour Scheme

Once I had realised the cause of the problem I also knew what I had to do: Change the colour scheme! Having bright outlines on a dark base plate should improve contrast and make the glowing letters look bold under all circumstances.

How about a base plate in dark red? Well, let’s try it out …

After removing the strips I sanded the base plate to get rid of any residue of glue.The sanded base plate was then painted dark red.

That looked promising! Now I needed to find a bright colour for the outlines. For the sake of simplicity – and because I really liked its look – I decided to try using the same colour (a bright warm yellow) I had used to paint the base plate initially.

Using removable glue I temporarily fixated the outlines on the base plate to get an impression of the final look.The outlines were painted yellow (the same colour I had initially used on the base plate)The complete sign in its new colour scheme.

Finally the sign started to look really gorgeous!

And, surprisingly enough, that’s how this story ends. The finished sign was mounted in our office kitchen, where it has been ever since:

Final (electrical) test of the completed sign.Power is provided by a 9V power adapter connected to the mains.

  1. Aka “using google to search for images of neon signs”. 

  2. For that I had to make most of the segments longer, not shorter, though. However, even if the longest segment was now too short to fit the longest stroke, I could still perfectly use it for the second longest stroke, then use the second longest segment for the third longest stroke and so on. In the end I only had to add one new segment, for the longest stroke. 

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